The present invention relates to a system for cleaning three-way valves.
Three-way valves are employed in various processes through which a liquid material is passed. A typical example of such processes is a heat-sterilization process for a liquid material such as milk, cream, soup, chowder, or the like and will be described hereinunder with reference to FIG. 1 of the accompanying drawings, which is a flow sheet of the heat-sterilization process for a liquid material wherein a liquid material is transferred by a pump 7 from a material supply tank 1 through a main pipe 2, and a first branch pipe 2a successively to a heat sterilizer 3, storage tank 4, a pipe 2b and a filling machine 5 to become the final product. In the event of a sterilization failure due to a reduction in the sterilization temperature in the sterilization process, the flow of liquid material through the main pipe 2 is returned through pipes 6 and 6a to the material supply tank 1 for a repeating sterilization. To this end, three-way valves 8 and 9 are operated to connect the main pipe 2 to the pipe 6 and to connect the pipe 6 to the pipe 6a.
Usually, this heat sterilization system is cleaned with a separate cleaning fluid, by circulating the cleaning fluid first through the main pipe 2, first branch pipe 2a, pipes 2b, 2c and the pipe 6a while operating the filling machine 5 and a return pump 11, and then through the main pipe 2 and the pipes 6 and 6a. To this end, the three-way valves 8 and 9 are operated in succession to form the above-mentioned flow paths of the cleaning fluid. Namely, for cleaning the flow path constituted by the main pipe 2, first branch pipe 2a, pipes 2b, 2c and the pipe 6a, the three-wave valve 8 is operated to allow the cleaning fluid to flow from the main pipe 2 to the first branch pipe 2a, while the other three-way valve 9 is operated to direct the cleaning fluid from the pipe 2c to the pipe 6a. During the cleaning of the pipes 2, 2a, 2b, 2c and 6a, the three-way valves are kept switched. In consequence, the old liquid material is inevitably left in small gaps between adjacent parts of each three-way valve. For instance, in a compression-type valve 8a as shown in FIG. 2, there is a small gap 27 between a bore in a valve housing and a valve stem 21 to permit the latter to move in the housing bore. During the operation of the system, therefore, the liquid material gradually invades this small gap 27 to deposit or accumulate on the valve stem 21, shaft seal 22 and the inner surface of bore 23 of the valve housing. On the other hand, in the case of a ball-type three-way valve as shown in FIG. 3 in which a ball valve member 24 is adapted to be rotated in a valve housing 25, the liquid material gradually comes into the gap 28 between the valve housing 25 and the ball valve member 24. With the cleaning method described hereinbefore, however, it is almost impossible to perfectly wash-away the old liquid material on these parts or in gaps. In order to perfectly wash the three-way valves, therefore, it is necessary to disassemble the three-way valve to permit the manual cleaning of independent parts. Obviously, this cleaning work is quite troublesome and time-consuming.
Hitherto, it has been proposed to clean the three-way valves with the cleaning fluid by operating repeatedly the three-way valves while circulating the cleaning fluid.
For instance, the following statement is made in ASTM Spec Tech Publ. (Am Soc Test Matter) No. 538 '73.
"All valves are operated 2 to 3 times during pre-cleaning, 4 to 6 times during cleaning and 3 to 4 times during post-cleaning. Thus, every portion of all valves and all parts of the piping system are subjected to mechanical and chemical processings. Consequently, by the operation of the valves, the pre-cleaning fluid or the cleaning fluid is introduced into the gland areas of respective valves thereby to effectively clean the seals, stems and the gland areas."
From this statement, it is understood that the three-way valve 8 of the system shown in FIG. 1 will be capable of being cleaned perfectly with the cleaning fluid by operating repeatedly the three-way valve 8 while circulating the cleaning fluid. However, in the heat-sterilization system of liquid material described above, the repeating operation of the three-way valves 8 and 9 causes the following problems. The cleaning fluid is directed alternatingly to the first branch pipe 2a and the pipe 6 so that the cleaning fluid can flow intermittently through each of these pipes 2a and 6. Namely, when the cleaning fluid is supplied to the pipe 6, the first branch pipe 2a cannot receive the cleaning fluid so that the filling machine 5 and a return pump 11 are made to idle unfavourably.
On the other hand, when the cleaning fluid is circulated through the pipes 2, 2a, 2b, 2c and 6a, the repeating operation of the three-way valve 9 results in intermittent blockade of the flow of the cleaning fluid through the pipe 2c to increase the pressure in the pipe 2c to a considerably high level, thereby incurring various problems such as leak of the cleaning fluid from, for example, the connections of the pipe 2c. At the same time, the return pump 11 and the filling machine 5 are overloaded to suffer from various troubles.